Species competitive ability growth rate as a function

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Species’ competitive ability – growth rate as a function of the resource that is  least available compared with the availability of all resources.  One Resource  Competition Rule  When two species compete for the same single limiting resource   species  with the lowest R* always wins.   Drives species to extinction by lowering resource availability so low that is  has negative growth rate.  Tilman Competition Model  Based on the differences in ability of species to grow at various levels of two  or more resources.   Uses “Zero Net Growth Isocline”.   o Made up of all combinations of the level of resource one and resource two at  which population growth of a species equals zero.  o Plot of R2 (y) vs. R1 (x). \ o ZNGIs are characteristics of species and have to  be determined empirically.   Consumption Vectors o Consumption vectors show change in resource  availability caused by consumption.   o The total amount of consumption depends on the consumption of each  individual and the number of individuals.   o Based on the net vectors of of R1 and R2. 
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Supply Vectors o Measure the rate of supply of resources in  the environment.   o The supply vectors depend on the current resource levels and the resource  supply point (S).   Measures the total amount of resources in an environment.   Resources can either be found in the environment or in living organisms.   S is a characteristic of the environment and can be measured.   The equilibrium resource level (E) occurs where consumption vectors and  supply vectors are equal and opposite. This is a stable equilibrium.   The species with the R* value farther from the origin is the one that is more  limited.   Coexistence is possible if there is a resource level in the environment at  which the growth rate of both species is equal to zero. This can only happen if the ZNGIs intersect.   The outcome of competition between two species when their ZNGIs intersect  depends on consumption vectors and the resource supply point.   Coexistence is only possible in regions 3, 4, or 5.   o In regions three and five, consumption moves resources so that one species  will win.   o In region four, equilibrium is possible:  Unstable equilibrium – when one species consumes the resources that limits  the other species more than the other resource. (vector is immediately next to the ZNGI).   Stable equilibrium occurs when one species consumes more of the resource  that limits itself than the other resource (vector is closer to the ZNGI of the  other species).  
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  • Summer '14
  • A.McIntoshandJ.Pinzon
  • Ecology, Interspecific competition, Tilman

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